1. Field
The disclosed concept relates generally to electrical switching apparatus and, more particularly, to electrical switching apparatus, such as circuit breakers. The disclosed concept also relates to linking assemblies for electrical switching apparatus.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions as detected, for example, by a trip unit.
FIGS. 1A-1D show one non-limiting example of a circuit breaker 1 (partially shown) including an operating mechanism 3 (shown in simplified form in FIG. 1A) having a linking assembly 5 that cooperates with a poleshaft 7 to open (e.g., separate) and/or close (e.g., electrically connect) the separable contacts 17 (shown in simplified form in FIG. 1A) of the circuit breaker 1. In the example of FIGS. 1A-1D, the linking assembly 5 cooperates with a spring charging assembly 9, although it will be appreciated that such linking assemblies (e.g., 5) can also be employed in a wide variety of different electrical switching apparatus (not shown), with or without such a charging mechanism.
Among other functions, the linking assembly 5 is intended to reduce the amount of force that is required to be exerted by the accessories (not shown) of the circuit breaker 1 to effectuate the desired circuit breaker tripping reaction. For example and without limitation, such an accessory might be employed under certain circumstances to pivot a D-shaft 19, thereby releasing a hatchet 21 of the linking assembly 5, or to otherwise actuate (e.g., move) one or more linking elements 21,23,25,27,29 of the linking assembly 5 and/or a corresponding portion of the circuit breaker operating mechanism 3 (FIG. 1A).
As shown in FIGS. 1C and 1D, in addition to the aforementioned hatchet 21, the example linking assembly 5 includes linking elements 23,25,27,29, resulting in three stages (e.g., labeled stage 1, stage 2 and stage 3 in FIGS. 1C and 1D) of force reduction. While this is sufficient for relatively large accessories capable of exerting substantial force, it is desirable to provide further force reduction so that existing, readily available and relatively small accessories can be employed. Providing such a force reduction is a significant design challenge as it generally requires unacceptable, unreliable or impossible toggle angles (e.g., angles between linking elements 23,25,27,29 of the linking assembly) in order to provide the desired motion among the hatchet 21, cradle 25 and linking elements 23,27,29.
There is, therefore, room for improvement in electrical switching apparatus, such as circuit breakers, and in linking assemblies therefor.